Electric delay system



Patented Apr. 28, 1953 ELECTRIC DELAY SYSTEM Myron E. Krom, Madison, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 21, 1950, Serial No. 202,066

Claims. 1

This invention relates to electrical systems and more particularly to a system for delaying the release time of electromagnetic apparatus.

It is frequently desirable to provide a delay interval between the occurrence of a control function and the release of an electromagnet in response thereto. This is conventionally accomplished either by modifying the electromagnetic structure per se or by associating a capacitor or a resistance-capacitance network with the winding of the electromagnet. It is well known that inaccuracies of timing are inherent in pragmatic utilizations of such devices. These inaccuracies accrue from the fact that the point to which the energizing current must be reduced to permit the release of conventional electromagnets varies over a relatively wide range on successive operations of the electromagnet, and from the fact that with capacitors of practical size, the slope of the charging-current-versus-time curve for the capacitor is small at the delay intervals normally required.

An object of this invention, therefore, is to improve the accuracy of time delay in a system for delaying the release of an electromagnet.

Another object of this invention is to render the time delay of a system for delaying the release of an electromagnet substantially independent of supply voltage variations.

A feature of this invention is the use of a unidirectional current conducting device sharply to cut off the charging current of a capacitor at a predetermined point of charge.

Another feature of this invention is the utilizing of the more nearly linear portion of the charging-current-versus-time curve of a capacitor to control the time delay of release of an electromagnet.

The manner in which the objects are attained, and the above and other features of the invention may be more fully understood from the following description of preferred embodiments thereof when read with reference to the accompanying drawings in which: I

' Fig. 1 is a representation of a preferred embodiment of the invention;

Fig, 2 represents a modified form of Fig. 1 showing the use of a double-wound relay to increase the accuracy of timin Fig. 3 represents another modified form of Fig. 1 showing the use of a different combination of sources of potential; and

Fig. 4 is a voltage-versus-time curve applicable to the circuits disclosed in Figs. 1 and 2.

In the several figures of the drawings, the correlative parts are given identical designations. Where numerical reference characters are em ployed, the hundreds digit thereof is modified in accordance with the figure number.

Referring now to Fig. l. of the drawings, relay T is provided with contacts which control an external load circuit. This relay is normally operatedf the energizing path therefor being trace- 2 able from ground at the back contact of normally unoperated start relay ST, conductor |0| winding of relay T and to the negative pole of the battery B, the positive pole of which is grounded.

Since ground is connected to conductor ill I, the right-hand electrode of capacitor C! is at ground potential. The left-hand electrode of capacitor CI is connected to ground through resistor RI and is connected to battery B through the unidirectional current conducting device V and through resistor R2. Device V may be a dry rectifier, a crystal rectifier, a vacuum tube or any other suitable type of unidirectional current conducting device having a loW forward resistance and a high inverse resistance. In accordance with the customary symbolism, the device V presents a low impedance to conventional current flow in the direction of the arrow, and presents a high impedance to conventional current flow in the opposite direction. Preferably the inverse resistance of the device V should be several times greater than the resistance of resistor RI.

Although the circuit comprising resistor R!, device V and resistor R2 will serve as a voltage divider since the potentials are applied in the proper direction for device V to be conductive, the value of resistor RI is preferably very much greater than the combinational value of resistor R2 and the forward resistance of device V and therefore the potential applied to the left-hand electrode of capacitor C! is substantially at, and for purposes of description may be considered to be at, the potential of battery B. As a result of the application of these potentials to capacitor C! during the period while relay ST is unoperated, capacitor Cl will attain a charge of negative E volts (the potential of negative battery B), with the left-hand electrode of capacitor Ci being at a potential negative relative to the potential at the right-hand electrode thereof. The condition of the left-hand electrode of capacitor Cl during this period is represented by the line from F to G on the graph of Fig. 4.

When it is desired to initiate the timed release of relay T, relay ST is operated. Relay ST, in operating, disrupts the previously traced energizing path for relay T and also removes the ground potential from the right-hand electrode of capacitor Cl. Therefore (ignoring the inductive effects of the winding of relay T) the potential at the right-hand electrode of capacitor C! momentarily becomes equal to the potential of battery B, i. e., a potential of negative E volts. Since capacitor Cl is charged to a potential of negative E volts and since the charge on a capacitor cannot instantly be changed, the lefthand electrode of capacitor Cl will immediately and momentarily change to a potential of negative 2E volts with respect to ground. This change in condition on the left-hand electrode of capacitor Cl is represented by the line from G to H on the graph of Fig. 4.

3 Therefore; at.-;.thisi instant, there" isza potential of negative"'2E volts in serieswiththe winding of relay T and resistor R l comprising the charge of negative E volts on capacitor CI in series with the negative E volt potential of battery-B.

consequence thereof, capacitorCi ,Will, in eifect, charge over a path from therightrhandelectrode.

of capacitor Cl, winding of relay .T, .battery..B,- ground, resistor Rl, to the left=hand electrode of capacitor Cl. This current flow is in-thesame direction through the winding of relayTr as was the original energizing current so relay '1 is held operated. :It will'beobserved that whenthelefthandeelectrode fcapacitor. Cl attains .a; potenitialuof negative 2E avolts, the unidirectional-.current. conducting device will be biased in: the nonconducting direction so the circuit comprising device V- and resistor R'ziwilhhave no appreciable effectfon the charging aof aca-pacitor .Cl over-the above-traced path. through the. winding iof relay-TI.

:Since capacitor Ci .isinitiallycharged to ..-a.

'valueof negative -:E rvolts, with .the left-hand --.-electrode thereof negative relative.to .-the..rightahand. electrode and. since: the; conditions v:subsequent .to the. operation .ofrelay ST. are-such. that ground. is :connectedto theleft-hand electrode rofccapacitorci through .resistor. RI andnega- -tive-zbatteryis.connected to the right-hand electrode l .ofcapacitor .Ci through the .winding of relay -T,-capacitor Cl willtend to charge ,to-a

potential of negative E volts in the opposite'direcvtion, .v-iz., with the l'right-hand electrode thereref-negative relative .to the left-hand electrode.

Ignoring for .the' present the. effect. of device .V ..on the operation. of the apparatus,.the change of condition of thesleit-handr electrode of ca-pacitor ..Ci during: this charging; period. is represented :by the-.line-from H to .M.on the graph oi..Fig. 4. Except.forr-thelinductive discharge of thewindingeot relay T, which .modifies .the curve. during the portion H .to-J, this. charge. will he expcnential; with the rateflofscharge being controlled es- :sentially-bythe value of .resistor R! .and ca- ,pacitor .Cl eitherorbothof which may bevaried totselect the desired delay. interval.

\ Continuing to ignore forthe' present theefiect of thedevice Von the operation oftheapparatus, letpit be assumed .that the current. through the winding .ofrelay will reach .a .sumciently i low .value to. permit the. release of relay .Tsomewhene vduring-the. range of times :anclpotentialsdesig- J 'natediLon. thegraph .of:Fig... Since-the value -;ofthe ;current at which. .a-.conventional :relay will release isnotrpreciseobut varies appreciably with variations in adiustment -voltage.andam- .bient. temperatura; the. time .variation Iduring-the .range marked L willbere-latively.largedue-ito ..the.-.reduced slope-poi.theccurrentfversusetime..or rvoltagewversusetime .curve during this period. .ilherefore, inaccuracies in timing result.

,Inaccordancewith the principleslof the present invention, means .are 5 provided for. sharply cutting. off-the charging current forcapacitor. Ci, .-and.thereforev for sharply. cutting. ofi the. holdinglcurrenttthrough. the Winding of relay at,-a point vwhere the current-versus-time .or voltageversus-time (curve. has. a. relatively large slope. The parameters. of the. circuit. are. .preferahlyse- .lectedsso that; the=-value of. current .at which .the said means-Hacts-to terminate thatcurrent flow .is .eqnalto orslightly greaterthan the deter-- mined .hold =..current value for 1 the particular ,,relay,.i...e., the minimum value of currentat which the relay mustihold .operated. -.On the 4 '-voltage=versus"-time graphicfFig.-;;4;this"point is "designated'K.

The means for performing this sharp cut-off of the holding current flow through the winding '55 rotjrelayiiTaby sharply cutting 01'1" the charging .current for .capacitor CI is the unidirectional .current conducting device V. As was noted here- .inbefore; wvhenJthe left-hand electrode of capacitor ,Cl .attainsa potential of negative 2E vo1ts,'the device V is rendered non-conductive sinceritstlower electrode is at a potential of a negative E volts. This condition of non-con- :ductivitywill continue asslongm as .the-uppereelec- .trodez-of. device V continues-tozbe at amore negative potential .ithanlthe. lowenelectrode. of. device .V, he; as long as the leftehandrelectrodelofzicaspacitor. Cl is more. negative .than .a negativerE volts. When.the left vhand electrode. of :capacitor 1; l reaches .a-potential of a negative E volts,. .defvice .1]. becomes conductiveand .the. chargingigcurlrentiorecapacitor ..CI is. immediately .cut eofi. .Since .the winding .ofrelay .T..is in theecharging oGiIiClliU for; capacitor C l the. holding. currentLfor relay T will also he (ignoring.theireactiveefiects ooflthe-windinglof relay immediately otermihated and relay T will release. As membeseen'in "the i graph of Fig; A, .the. left-hand. electrode '..of ..capacitor C I reaches. a. potential loiasnegativeii volts at .point .K,..and.therefore the potential at .that electrodeis; heldtat that, potential as islrepresented ..by -the: line..from.K-to;;N.

.. It will be noted that capacitoriC.[Lhaaamfic-.

tive. chargeof. E yolts. inone. direction; atppoint H on the curve of Fig. 4, that capacitor iClI-has lcapacitor C I ,1 if device iv i were anot .fiective.-to

prevent it, -would .zapproach. aechargekofiEnvolts .inthe opposite.directionLbeyorid,pointlMQonlthe curve-.of .Eig.-.-.4. oThe .entireizhangein potential difference ..across..,capacitor .01 Q from point .H. 3120 point M on the curvemaylbe.considereditobega .charging. of .that capacitor, or; if 'desired, this ,change. maybe. considered to .be a dischargeifrom .pointfI-I. to, point. :Kland. a chargeifrom pointiK to point M.

v It will-.be. notedthat. asin'gle source .OfgpOten- ,tial'iB controls the. initial charge on capacitor C l and the pointat which. deviceiVsubseguently again becomes conductive. Therefore, .;even

5r; though the supply voltage varies within reasonable .limitsbetween successive utilizations .ofgithe apparatus, .the delayinterval .w'ilLremainz: constant..

When;relay;..ST is operated-,Lahighifrequency .negativepiflse will or ,may1be;generatedjas;a.ire sult of the inductive characteristicsofthe winding of relay .T. .This..pulsenzillor.maymass cazpacitor Cl and be applied to the devicelV. ".Withjcertain types of unidirectional.current condi1cting. .i1devices. suchas. seleriiumoxide :rectifiers,=-this1volt.-

age surge may not.cause;a1breakdowngofithe device. ...However, with..other' types -ofurectiiying device; such as germanium .rectifiers thislvoltage surge may possibly cause .the ..device .tolbreak .down in the inverse. direction. .CapacitorjC2may be placed in parallel withthe jdevice-.V; to. obviate the possibility ofsuch .maliunctioningnccurring.

-When. relay-.STis released preparatory. to the initiation of another. cycle of 1 operation .of .the apparatus, relaylT. will again operate and capacir tor Cl will again .becomeacharged. .Itwillilb'e noted that. the. operate time of; relay .fIiisnote-im creased by. the presence. of. the other. circuit .elements.

JIZhe circuiteofiEigs 2. is..identical...to; them-circuit substantially .no -charge at point .K, -andithat' of Fig. 1 except that resistor R2 is replaced by an opposing secondary or release winding of relay T. The circuit of Fig. 2 functions identically to the circuit of Fig. 1 up to the point where device V is rendered conductive. At that time, current will flow from ground, resistor RI device V, secondary winding of relay T and to grounded battery 3. As a result, a negative flux is in duced in relay '1 causing the relay rapidly to release. This provides a substantial reduction of any errors which may arise from variations of the physical release time of the relay per se.

The potentials applied to the circuit may be of either polarity and of any suitable value. One of the plural possible variations of the basic circuit of Fig. 1 is shown in Fig. 3. The circuit of Fig. 3 is identical to the circuit of Fig. 1 except that battery B and ground have been interchanged in each case, except that a current limiting resistor R3 has been added as a safety measure, and except that the polarity of the rectifying device V has been reversed. Taking these modifications into consideration, the modus operandi of the circuit of Fig. 3 is as that above described in relation to Fig. 1. Capacitor C! in Fig. 3 is initially charged to substantially E volts, with the right-hand electrode thereof being negative with respect to the left-hand electrode; upon the operation of relay ST, the effective potential at each electrode of capacitor Cl is raised by E volts whereby the left-hand electrode of capacitor CI momentarily assumes the potential of substantially a positive E volts whereby rectifier V is biased to a non-conducting state; capacitor Cl charges towards an ultimate condition wherein its left-hand electrode would be at a potential of negative E volts, and E volts negative relative to the right-hand electrode thereof; but at the time during that charging period at which the left-hand electrode of capacitor C! assumes an effective potential of ground, device V is rendered conductive to terminate the charging of capacitor Cl and to cause the release of relay T. In a manner similar to that in which the variation of potential at the left-hand electrode of capacitor CI of Fig. 1 was represented in Fig. 4, so the variation of potential at the left-hand electrode of capacitor C! in Fig. 3 may be represented by inverting the representation of Fig. 4, labeling point F thereon ground, labeling point H thereon positive E volts and by utilizing a line at negative E volts as the asymptote of the curve K-M.

It is to be understood that the above-described arrangements are but illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. In a timing apparatus, a relay, a switch, a capacitor connected to the winding of said relay, means including said switch for establishing an initial potential condition on said capacitor, means operative under the control of said switch for changing the potential condition of said capacitor and for causing current to flow in a circuit including said capacitor and the winding of said relay, and a unidirectional current conducting device connected to said capacitor and operative when said capacitor attains a preselected potential condition for abruptly terminating the flow of current through said relay.

2. In a timing apparatus, a relay, a normally effective operating circuit for said relay, a capacitor connected to said operating circuit, means for establishing an initial potential condition on said capacitor, a potential-condition changing circuit for said capacitor including the winding of said relay, a switch for simultaneously interrupting said operating circuit and for enabling said potential-condition changin circuit, and a unidirectional current conducting device connected to said capacitor and operative when said capacitor attains a preselected potential-condition for abruptly disabling said potential-condition changing circuit.

3. In a timing apparatus, a relay, a normally effective operating circuit for said relay, a capacitor having one electrode connected to said operating circuit, a unidirectional current conducting device connected to the other electrode of said capacitor, means including said device for establishing an initial potential condition on said capacitor, a potential-condition changing circuit for said capacitor including the winding of said relay, a switch for simultaneously interrupting said operating circuit and for enabling said potential-condition changing circuit, and means including said device effective when said cap-acitor attains a preselected potential condition for abruptly disabling said potential-condition changing circuit.

4. In a timing apparatus, a relay having an operating winding and an opposing winding; 2. first series circuit comprising a source of potential, a resistor, a unidirectional current conducting device and the opposing winding of said relay; a second series circuit comprising a source of potential, a switch and the operating winding of said relay; a capacitor having two electrodes; a connection between one electrode of said capacitor and a point in said first series circuit intermediate said resistor and said device; and a connection between the other electrode of said capacitor and a point in said second series circuit intermediate said switch and the operating winding of said relay.

5. In a timing apparatus, a relay, a switch, a capacitor, a normally effective operating circuit for said relay including said switch, means including said switch and a unidirectional current conducting device for establishing an initial potential condition on said capacitor, a normally ineffective potential-condition changing circuit for said capacitor for holding said relay operated including said capacitor, the winding of said relay and a resistor, said switch being effective simultaneously to disable said operating circuit and to enable said potential-condition changing circuit, and means comprising said device effective when said capacitor attains a preselected potential condition for abruptly disabling said p0- tential-condition changing circuit MYRON E. KROM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,762,811 Charlton June 10, 1930 2,049,376 Hertwig July 28, 1936 2,111,632 Kannenberg Mar. 22, 1938 2,114,016 Dimond Apr. 12, 1938 2,299,941 Townsend Oct. 2'7, 1912 2,342,821 Reagan Feb. 29, 1944 2,429,819 Jordan Oct. 28, 1947 

